Inhibition of DNA degradation (DNA protection) in UV damaged cells of E. coli is thought to result from the production of an inhibitor which either protects single stranded regions of DNA or blocks the action of exonucleases, primarily ExoV, directly. Induction of the inhibitor of ExoV depends upon two genes, recA and lexA. Current hypotheses state that high levels of recA protein are expressed after UV damage. The levels of recA protein are sufficiently high to allow it to bind and protect the many single stranded regions present after replication of damaged DNA. Our previous studies have shown that rnmA mutant strains are not defective in ExoV activity nor do they produce high levels of recA protein either constitutively or after DNA damaging treatment. Nonetheless, rnmA strains do not degrade their DNA after UV irradiation. We are examining the nature of DNA protection after irradiation in rnmA strains, identifying the genes responsible and the proteins they produce. Since the recA gene is known to possess regulatory properties the possibility exists that its role in postirradiation DNA protection in wild type strains is regulational rather than functional. These experiments will provide us with an opportunity to examine this question.